Testing the Efficacy of Topical Calcipotriene Plus 5-Fluorouracil Combination to Activate the Immune System Against Precancerous Skin Lesions in Organ Transplant Recipients

Inclusion Criteria: * Patients who had received a kidney or lung transplant \>= 2 years before enrollment in the study with a stable status of transplanted graft (participants must have visited their transplant specialist within 6 months before enrolling to the study, documenting stable graft safety). The target population includes patients who are on tacrolimus and/or MMF without voriconazole as their immunosuppressive regimen. * Presence of four to fifteen clinically typical, visible, and discrete AKs in 25 cm\^2 on any of the following anatomical sites: upper extremities, face, and/or scalp. * Age of at least 18 years. Because no dosing or adverse event (AE) data are currently available on the use of calcipotriene plus 5-FU in participants \<18 years of age, children and adolescents are excluded from this study but will be eligible for future pediatric trials, if applicable. * Karnofsky performance status \>= 60%. * Leukocytes \>= 3,000/microliter and \< 12000/ microliter. * Absolute neutrophil count \>= 1,000/microliter. * Platelets \>= 100,000/microliter. * Creatinine =\< 1.5 × institutional upper limit of normal. * Baseline respiratory requirement for lung transplant recipients: * Respiratory rate within 12-18/min * PO2 saturation within 90-100mmHg * Female participants must be non-reproductive potential (i.e., post-menopausal by a history of age \> 50 years old and no menses for \>= 1 year without an alternative medical cause; OR history of hysterectomy, history …